The Joint Strike Fighter (JSF) stealth jet that Israel wants to purchase from the United States is years behind schedule and will likely cost over 40 percent more than initially predicted, a report released by the United States Congress's General Accountability Office (GAO) has revealed.

According to the report, which was released over the weekend, the development of the JSF - also known as the F-35 - will cost more and take longer to complete than reported to the Congress in April 2008, primarily because of cost overruns and extended time needed to complete flight testing.

"Total development costs are projected to increase between $2.4 billion and $7.4b. and the schedule for completing system development extended from 1 to 3 years," the GAO, Congress's audit and investigative arm, wrote in a report submitted to the Subcommittee on Air and Land Forces.

The increase in costs was caused by delays in manufacturing test aircraft as well as cost overruns on both the aircraft and engine contracts, the report said.

The jet is manufactured by Lockheed Martin and current estimates are that the asking price from Israel will be close to $200 million per aircraft.

The report also stated that manufacturing inefficiencies and shortages in certain parts had delayed the completion and delivery of aircraft needed for testing.

"The contractor has not yet demonstrated mature manufacturing processes, or an ability to produce aircraft consistently at currently planned annual rates," the report stated.

While it is unclear what impact the report would have on Israel's evaluation of the aircraft - the IAF has received Pentagon approval to purchase up to 75 aircraft in a deal that could reach $15b. - the Defense Ministry is currently in advanced negotiations with the US regarding its demand to integrate Israeli technology into the aircraft.